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Methylpropane, (CH₃)₂CHCH₃, is an isomer of butane, CH₃(CH₂)₂CH₃.
(a)
(i) Explain why methylpropane and butane are a pair of isomers.
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(ii) Identify the type of isomerism shown by methylpropane and butane.
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(b) When a sample of butane is heated to 373 K, in the presence of a catalyst, and allowed to reach equilibrium the following reaction occurs.
CH₃(CH₂)₂CH₃(g) ⇌ (CH₃)₂CHCH₃(g) ΔH = -8.0 kJ mol⁻¹
State and explain the effect on the composition of this equilibrium mixture when the temperature is increased to 473 K.
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(c) 1 mole of butane gas was added to a 1 dm³ closed system, at a constant temperature and pressure. The amount of butane and methylpropane was measured at regular time intervals.
(i) Label the graph with a t to show the time taken to reach dynamic equilibrium. [1]
(ii) Use the graph to find the concentration of butane and methylpropane in the mixture at equilibrium.
concentration of butane = ................................ mol dm⁻³
concentration of methylpropane = ........................ mol dm⁻³ [1]
(iii) Write an expression for Kₜ for this reaction. [1]
(iv) Calculate a value for Kₜ and state its units.
Kₜ = .................................... units = .................................... [2]
546
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Group 17 elements are commonly referred to as the halogens.
(a) State and explain the trend in volatility of chlorine, bromine and iodine down the group.
Hydrogen gas reacts with the different halogens under different conditions.
(b) (i) State the conditions required for chlorine to react with hydrogen at room temperature.
(ii) On heating, iodine reacts with hydrogen in a reversible reaction.
Give the equation for this reaction. Include state symbols.
(c) Hydrogen chloride reacts with water.
\[ HCl + H_2O \rightarrow H_3O^+ + Cl^- \]
(i) In this reaction, one of the reactants behaves as a Brønsted-Lowry acid.
What is meant by the term $\text{Brønsted-Lowry acid}$ ?
(ii) Identify the reactant behaving as an acid and its conjugate base.
(iii) Name the type of bond formed between \( H^+ \) and \( H_2O \) to make \( H_3O^+ \).
(iv) For \( H_3O^+ \), predict its shape and the $\text{H–O–H}$ bond angle.
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Period 3 elements react with chlorine gas, $Cl_2(g)$, to form chlorides.
(a) The table shows the differences in observations which occur when two Period 3 chlorides are added to water.
| Period 3 chloride | observations when added to water | pH of solution formed with water |
|---|---|---|
| NaCl | White solid disappears. Colourless solution made. | 7 |
| SiCl_4 | Pale yellow solution forms. Bubbles form and the test-tube feels hot. White precipitate forms. | 1–2 |
(i) Write an equation for the reaction occurring when $SiCl_4$ is added to cold water. Include state symbols. [1]
(ii) Name the type of reaction occurring when $SiCl_4$ is added to water. Ignore the exothermic/endothermic nature of the reaction. [1]
(iii) Explain, in terms of bonding, why $NaCl$ and $SiCl_4$ behave differently when added to water. [2]
(iv) Explain, in terms of electronegativity, why the bonding in $NaCl$ is different from the bonding in $SiCl_4$. [3]
(b) $Cl_2(g)$ dissolves in cold water and reacts with it.
$Cl_2 + H_2O \rightarrow HCl + HClO$
(i) Identify the oxidation number of chlorine in each of the chlorine-containing species in this reaction.
| chlorine-containing species | $Cl_2$ | $HCl$ | $HClO$ |
|---|---|---|---|
| oxidation number of chlorine |
[2]
(ii) Name the type of reaction occurring. [1]
(iii) Explain why chlorine is used in the purification of water. [1]
(c) A mixture of $HCl$ and $HClO$ is added to cold dilute $NaOH$. One of the products behaves as a bleach.
Suggest the equation for the reaction occurring.
[2]
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There are many different types of aliphatic and aromatic hydrocarbons.
(a) Name a naturally occurring source of aliphatic and aromatic hydrocarbons and outline how different hydrocarbons are separated from this source.
name of source ...............................................
outline of separation of hydrocarbons ...............................................
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(b) When alkanes are heated to high temperatures, in the absence of air, the molecules can break into smaller molecules.
(i) Identify the type of reaction occurring.
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(ii) Write an equation which describes the reaction occurring when heptane, $C_7H_{16}$, is heated in the absence of air, to form hexane, butane and ethene only.
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(c) The equation for the complete combustion of ethene is shown.
$$C_2H_4 + 3O_2 \rightarrow 2CO_2 + 2H_2O$$
Calculate the volume, in dm$^3$, of carbon dioxide formed in the complete combustion of 1.00 g of ethene at room temperature and pressure.
volume of $CO_2$ = .............................. dm$^3$ [3]
The table compares the reactivity of alkanes and alkenes with chlorine.
[Table_1]
(i) During the first stage in the substitution reaction chlorine forms chlorine free radicals.
Explain what is meant by the term free radical.
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(ii) Name and explain the type of bond breaking which occurs to form chlorine free radicals.
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(iii) Name the stage of the reaction mechanism which occurs when a methane molecule reacts with a chlorine free radical.
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(iv) Complete the equation for the reaction which occurs when a methane molecule reacts with a chlorine free radical.
$$\text{H}\quad \text{H–C–H}\quad + \cdot \text{Cl} \rightarrow\quad + \quad \text{H}\cdots \quad\cdots [1]$$
(v) Carbon atoms can form σ and π bonds within hydrocarbon molecules.
Explain the following statement with reference to σ and π bonds.
Alkenes react with electrophiles but alkanes do not.
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[2]
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(a) The structure of ester V is shown.
(i) Name V.
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V reacts with a reagent to form a salt of a carboxylic acid and an alcohol.
(ii) Identify a reagent that could be used in this reaction.
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(iii) Draw the displayed formula of the alcohol made during this reaction.
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(iv) State one other possible use for V, apart from as a food flavouring.
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(b) Ester W is made up of 54.5% carbon, 9.1% hydrogen and 36.4% oxygen.
(i) Calculate the empirical formula of W.
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(ii) State what additional information is required to determine the molecular formula of W.
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(c) Compounds X, Y and Z are shown. They all have the same molecular formula.
(i) Deduce the molecular formula of X, Y and Z.
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(ii) In three experiments, sodium is added to separate samples of X, Y and Z.
Complete the table to show the observations for each of these three experiments. Ignore any temperature changes which may occur.
[Table_1]
experiment observations
Na + X
Na + Y
Na + Z
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(d) Sodium carbonate solution reacts with methanoic acid.
Write the equation for this reaction.
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